The surrounding passage is worth reading in full. Seneca writes to Lucilius about the habit of saving life for later — accumulating it rather than spending it, treating the present as a corridor between a past that is finished and a future that will eventually be worth inhabiting.

The argument is not that you should act impulsively or abandon planning. It is that the orientation of waiting — for the right conditions, for the right moment, for the thing you are currently doing to be out of the way — is itself a way of spending time, and not a neutral one.

The letter is only a page long. It rewards reading every few years.